Heat source options for a mobile home

We have 7 mobile homes in our park that we are rehabbing and all will need new heaters. Has anyone tried any options for heating instead of the central heat which seems to run about $1000-$1300 each. Our park is in Southwest Oklahoma where it only gets cold for a few months out of the year. We are also needing to get window AC units so I thought about getting the combo window ac/ heat units. Or maybe one gas wall heater for the family room then a window unit for the bedrooms. Any money saving suggestions would be greatly appreciated.